2xxx series aluminum lithium alloys

ABSTRACT

Wrought 2xxx aluminum lithium alloy products having a thickness of from 0.040 inch to 0.500 inch are disclosed. The wrought aluminum alloy products contain from 3.00 to 3.80 wt. % Cu, from 0.05 to 0.35 wt. % Mg, from 0.975 to 1.385 wt. % Li, wherein −0.3*Mg−0.15Cu+1.65≦Li≦−0.3*Mg−0.15Cu+1.85, from 0.05 to 0.50 wt. % of at least one grain structure control element, wherein the grain structure control element is selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 1.0 wt. % Zn, up to 1.0 wt. % Mn, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.15 wt. % Ti, up to 0.10 wt. % of any other element, with the total of these other elements not exceeding 0.35 wt. %, the balance being aluminum.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Provisional Patent Application No. 61/684,268, entitled “2XXX SERIES ALUMINUM LITHIUM ALLOYS”, filed Aug. 17, 2012, and which is incorporated herein by reference in its entirety.

BACKGROUND

Aluminum alloys are useful in a variety of applications. However, improving one property of an aluminum alloy without degrading another property often proves elusive. For example, it is difficult to increase the strength of an alloy without decreasing the toughness of an alloy. Other properties of interest for aluminum alloys include corrosion resistance and fatigue crack growth rate resistance, to name two.

SUMMARY OF THE INVENTION

Broadly, the present patent application relates to wrought 2xxx aluminum lithium alloy products having improved properties. Generally, the wrought 2xxx aluminum lithium alloy products have 3.0 to 3.8 wt. % Cu, 0.05 to 0.35 wt. % Mg, 0.975 to 1.385 wt. % Li, where −0.3*Mg−0.15Cu+1.65≦Li≦−0.3*Mg−0.15Cu+1.85, 0.05 to 0.50 wt. % of a grain structure control element selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 1.0 wt. % Zn, up to 1.0 wt. % Mn, up to 0.15 wt. % Ti, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.10 wt. % of any other element, with the total of these other elements not exceeding 0.35 wt. %, the balance being aluminum. Wrought products incorporating such alloy compositions may achieve improved properties.

The wrought products are generally in the form of sheet or thin plate having a thickness of from about 0.040 inch to about 0.500 inch. In one embodiment, the wrought aluminum alloy product has a thickness of at least 0.050 inch. In another embodiment, a thick wrought aluminum alloy product has a thickness of at least 0.060 inch. The improved properties described herein may be achieved with thick wrought products having a thickness of up to 0.400 inch, or up to 0.300 inch, or up to 0.250 inch. As used in this paragraph, thickness refers to the minimum thickness of the product, realizing that some portions of the product may realize slightly larger thicknesses than the minimum stated.

Composition limits of several alloys useful in accordance with the present teachings are disclosed in Tables 1a-1c, below (values in weight percent).

TABLE 1a EXAMPLE COMPOSITION OF ALLOYS Alloy Cu Mg Li Cu—Mg—Li Relationship Broad 3.0-3.8 0.05-0.35 0.975-1.385 −0.3 * Mg − Pref. (1) 3.1-3.7 0.10-0.30 1.005-1.355 0.15Cu + 1.65 ≦ Pref. (2) 3.2-3.6 0.15-0.25 1.035-1.325 Li ≦ Pref. (3) 3.3-3.6 0.15-0.25 1.035-1.310 −0.3 * Mg − 0.15Cu + 1.85

TABLE 1b EXAMPLE COMPOSITION OF ALLOYS Grain Structure Alloy Mn Control Ti Zn Broad   0-1.0 0.05-0.50   0-0.15 0-1.0 Pref. (1) 0.10-0.80 0.05-0.20 Zr   0-0.10 0-1.0 Pref. (2) 0.20-0.60 0.07-0.14 Zr 0.01-0.06 0-1.0 Pref. (3) 0.20-0.40 0.08-0.13 Zr 0.01-0.03 0-1.0

TABLE 1c EXAMPLE COMPOSITION OF ALLOYS Other Elements Alloy Fe Si Ag Each/Total Balance Broad ≦0.15 ≦0.12 Include in 0.10/0.35 Al “Other Elements” Pref. (1) ≦0.12 ≦0.10 Include in 0.05/0.15 Al “Other Elements” Pref. (2) ≦0.08 ≦0.06 Include in 0.05/0.15 Al “Other Elements” Pref. (3) ≦0.05 ≦0.04 Include in “ 0.03/0.10 Al Other Elements”

Copper (Cu) is included in the new alloy, and generally in the range of from 3.0 wt. % to 3.8 wt. % Cu. In one embodiment, the new alloy includes at least 3.1 wt. % Cu. In other embodiments, the new alloy may include at least 3.2 wt. % Cu, or at least 3.3 wt. % Cu, or at least 3.35 wt. % Cu, or at least 3.4 wt. % Cu. In one embodiment, the new alloy includes not greater than 3.75 wt. % Cu. In other embodiments, the new alloy may include not greater than 3.7 wt. % Cu, or not greater than 3.65 wt. % Cu, or not greater than 3.6 wt. % Cu.

Magnesium (Mg) is included in the new alloy, and generally in the range of from 0.05 wt. % to 0.35 wt. % Mg. In one embodiment, the new alloy includes at least 0.10 wt. % Mg. In other embodiments, the new alloy may include at least 0.15 wt. % Mg. In one embodiment, the new alloy includes not greater than 0.35 wt. % Mg. In other embodiments, the new alloy may include not greater than 0.30 wt. % Mg, or not greater than 0.25 wt. % Mg.

Lithium (Li) is included in the new alloy, and generally in the range of from 0.975 wt. % to 1.385. In one embodiment, the new alloy includes at least 1.005 wt. % Li. In other embodiments, the new alloy may include at least 1.035 wt. % Li, or at least 1.050 wt. % Li, or at least, or at least 1.065 wt. % Li, or at least 1.080 wt. % Li, or at least 1.100 wt. % Li, or at least 1.125 wt. % Li, or at least 1.150 wt. %. In one embodiment, the new alloy includes not greater than 1.355 wt. % Li. In other embodiments, the new alloy includes not greater than 1.325 wt. % Li, or not greater than 1.310 wt. %, or not greater than 1.290 wt. % Li, or not greater than 1.270 wt. % Li, or not greater than 1.250 wt. % Li.

The combined amounts of Cu, Mg, and Li may be related to realization of improved properties. In one embodiment, the aluminum alloy includes Cu, Mg, and Li per the above requirements, and in accordance with the following expression:

−0.3*Mg−0.15Cu+1.65≦Li≦−0.3*Mg−0.15Cu+1.85  (1)

In other words:

Li_(min)=1.65−0.3(Mg)−0.15(Cu); and  (2)

Li_(max)=1.85−0.3(Mg)−0.5(Cu)  (3)

Aluminum alloy products having an amount of Cu, Mg, and Li falling within the scope of these expressions may realize an improved combination of properties (e.g., an improved strength-toughness relationship).

Zinc (Zn) may optionally be included in the new alloy and up to 1.0 wt. % Zn. In one embodiment, the new alloy includes at least 0.20 wt. % Zn. In one embodiment, the new alloy includes at least 0.30 wt. % Zn. In one embodiment, the new alloy includes not greater than 0.50 wt. % Zn. In another embodiment, the new alloy includes not greater than 0.40 wt. % Zn.

Manganese (Mn) may optionally be included in the new alloy, and in an amount up to 1.0 wt. %. In one embodiment, the new alloy includes at least 0.05 wt. % Mn. In other embodiments, the new alloy includes at least 0.10 wt. % Mn, or at least 0.15 wt. % Mn, or at least 0.2 wt. % Mn. In one embodiment, the new alloy includes not greater than 0.8 wt. % Mn. In other embodiments, the new alloy includes not greater than 0.7 wt. % Mn, or not greater than 0.6 wt. % Mn, or not greater than 0.5 wt. % Mn, or not greater than 0.4 wt. % Mn. In the alloying industry, manganese may be considered both an alloying ingredient and a grain structure control element—the manganese retained in solid solution may enhance a mechanical property of the alloy (e.g., strength), while the manganese in particulate form (e.g., as Al₆Mn, Al₁₂Mn₃Si₂—sometimes referred to as dispersoids) may assist with grain structure control. However, since Mn is separately defined with its own composition limits in the present patent application, it is not within the definition of “grain structure control element” (described below) for the purposes of the present patent application.

The alloy may include 0.05 to 0.50 wt. % of at least one grain structure control element selected from the group consisting of zirconium (Zr), scandium (Sc), chromium (Cr), vanadium (V) and/or hafnium (Hf), and/or other rare earth elements, and such that the utilized grain structure control element(s) is/are maintained below maximum solubility. As used herein, “grain structure control element” means elements or compounds that are deliberate alloying additions with the goal of forming second phase particles, usually in the solid state, to control solid state grain structure changes during thermal processes, such as recovery and recrystallization. For purposes of the present patent application, grain structure control elements include Zr, Sc, Cr, V, Hf, and other rare earth elements, to name a few, but excludes Mn.

The amount of grain structure control material utilized in an alloy is generally dependent on the type of material utilized for grain structure control and/or the alloy production process. In one embodiment, the grain structure control element is Zr, and the alloy includes from 0.05 wt. % to 0.20 wt. % Zr. In another embodiment, the alloy includes from 0.05 wt. % to 0.15 wt. % Zr. In another embodiment, the alloy includes 0.07 to 0.14 wt. % Zr. In another embodiment, the alloy includes 0.08-0.13 wt. % Zr. In one embodiment, the aluminum alloy includes at least 0.07 wt. % Zr. In another embodiment, the aluminum alloy includes at least 0.08 wt. % Zr. In one embodiment, the aluminum alloy includes not greater than 0.18 wt. % Zr. In another embodiment, the aluminum alloy includes not greater than 0.15 wt. % Zr. In another embodiment, the aluminum alloy includes not greater than 0.14 wt. % Zr. In another embodiment, the aluminum alloy includes not greater than 0.13 wt. % Zr.

The alloy may include up to 0.15 wt. % Ti cumulatively for grain refining and/or other purposes. Grain refiners are inoculants or nuclei to seed new grains during solidification of the alloy. An example of a grain refiner is a 9.525 mm rod comprising 96% aluminum, 3% titanium (Ti) and 1% boron (B), where virtually all boron is present as finely dispersed TiB₂ particles. During casting, the grain refining rod is fed in-line into the molten alloy flowing into the casting pit at a controlled rate. The amount of grain refiner included in the alloy is generally dependent on the type of material utilized for grain refining and the alloy production process. Examples of grain refiners include Ti combined with B (e.g., TiB₂) or carbon (TiC), although other grain refiners, such as Al—Ti master alloys may be utilized. Generally, grain refiners are added in an amount ranging from 0.0003 wt. % to 0.005 wt. % to the alloy, depending on the desired as-cast grain size. In addition, Ti may be separately added to the alloy in an amount up to 0.15 wt. %, depending on product form, to increase the effectiveness of grain refiner, and typically in the range of 0.01 to 0.03 wt. % Ti. When Ti is included in the alloy, it is generally present in an amount of from 0.01 to 0.10 wt. %. In one embodiment, the aluminum alloy includes a grain refiner, and the grain refiner is at least one of TiB₂ and TiC, where the wt. % of Ti in the alloy is from 0.01 to 0.06 wt. %, or from 0.01 to 0.03 wt. %.

The aluminum alloy may include iron (Fe) and silicon (Si), typically as impurities. The iron content of the new alloy should generally not exceed 0.15 wt. %. In one embodiment, the iron content of the alloy is not greater than 0.12 wt. %. In other embodiments, the aluminum alloy includes not greater than 0.10 wt. % Fe, or not greater than 0.08 wt. % Fe, or not greater than 0.05 wt. % Fe, or not greater than 0.04 wt. % Fe. Similarly, the silicon content of the new alloy should generally not exceed 0.12 wt. %. In one embodiment, the silicon content of the alloy is not greater than 0.10 wt. % Si, or not greater than 0.08 wt. % Si, or not greater than 0.06 wt. % Si, or not greater than 0.04 wt. % Si, or not greater than 0.03 wt. % Si.

In some embodiments of the present patent application, silver (Ag) is considered an impurity, and, in these embodiments, is included in the definition of “other elements”, defined below, i.e., is at an impurity level of 0.10 wt. % or less, depending on which “other element” limits are applied to the alloy. In other embodiments, silver is purposefully included in the alloy (e.g., for strength) and in an amount of from 0.11 wt. % to 0.50 wt. %.

The new 2xxx aluminum lithium alloys generally contain low amounts of “other elements” (e.g., casting aids and impurities, other than the iron and silicon). As used herein, “other elements” means any other element of the periodic table except for aluminum and the above-described copper, magnesium, lithium, zinc, manganese, grain structure control elements (i.e., Zr, Sc, Cr, V Hf, and other rare earth elements), iron and/or silicon, as applicable, described above. In one embodiment, the new 2xxx aluminum lithium alloys contain not more than 0.10 wt. % each of any other element, with the total combined amount of these other elements not exceeding 0.35 wt. %. In another embodiment, each one of these other elements, individually, does not exceed 0.05 wt. % in the 2xxx aluminum lithium alloy, and the total combined amount of these other elements does not exceed 0.15 wt. % in the 2xxx aluminum lithium alloy. In another embodiment, each one of these other elements, individually, does not exceed 0.03 wt. % in the 2xxx aluminum lithium alloy, and the total combined amount of these other elements does not exceed 0.10 wt. % in the 2xxx aluminum lithium alloy.

The new alloys may be used in all wrought product forms, including plate, forgings and extrusions.

The new alloy can be prepared into wrought form, and in the appropriate temper, by more or less conventional practices, including direct chill (DC) casting the aluminum alloy into ingot form. After conventional scalping, lathing or peeling (if needed) and homogenization, which homogenization may be completed before or after scalping, these ingots may be further processed by hot working the product. The product may then be optionally cold worked, optionally annealed, solution heat treated, quenched, and final cold worked. After the final cold working step, the product may be artificially aged. Thus, the products may be produced in a T3 or T8 temper.

Unless otherwise indicated, the following definitions apply to the present application:

“Wrought aluminum alloy product” means an aluminum alloy product that is hot worked after casting, and includes rolled products (sheet and thin plate), forged products, and extruded products.

“Forged aluminum alloy product” means a wrought aluminum alloy product that is either die forged or hand forged.

“Solution heat treating” means exposure of an aluminum alloy to elevated temperature for the purpose of placing solute(s) into solid solution.

“Hot working” means working the aluminum alloy product at elevated temperature, generally at least 250° F.

“Cold working” means working the aluminum alloy product at temperatures that are not considered hot working temperatures, generally below about 250° F.

“Artificially aging” means exposure of an aluminum alloy to elevated temperature for the purpose of precipitating solute(s). Artificial aging may occur in one or a plurality of steps, which can include varying temperatures and/or exposure times.

These and other aspects, advantages, and novel features of this new technology are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the following description and figures, or may be learned by practicing one or more embodiments of the technology provided for by the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are graphs illustrating the performance of Alloy A of Example 1.

DETAILED DESCRIPTION

An example alloy (Alloy A) was cast as ingot and homogenized. The composition of Alloy A is shown in Table 1, below.

TABLE 1 COMPOSITION OF ALLOY A Al- loy Si Fe Cu Mg Mn Zn Ti Zr Ag Li A 0.018 0.027 3.50 0.21 0.30 0.35 0.019 0.130 — 1.18

Alloy A was then hot rolled to a gauge of 2.5 inch, after which it was solution heat treated and quenched, and then stretched, and then artificially aged to a T8 temper. A portion of this plate (17 inches by 14.5 inches) was then heated to about 900° F., and then processed to a final thickness of 0.125 inch using the following process:

-   -   The material was first hot rolled and the first two hot rolling         passes were in the transverse direction to broaden the sheet to         19 in. wide and the material was hot rolled in 10 rolling passes         to a thickness of approximately 0.25 in. Following hot rolling         the material was anneal at 800° F. for 4 hours, then cooled 50°         F./hr to room temperature. After annealing the material was cold         rolled to a final thickness of 0.125 in.

Following rolling, the material was solution heat treated and quenched, and then stretched about 3% (L direction). The material was then artificially aged for two times (about 24 hours and about 48 hours) at 290° F. Mechanical properties were then measured, the results of which are shown in Table 2, below (values average of duplicate specimens). Strength testing was conducted in accordance with ASTM E8 and B557. The fracture toughness was measured in accordance with ASTM E561 and ASTM B646 using middle cracked tension M(T) specimens. Specimens were in the T-L and L-T orientations and have a nominal 2a/W=0.25. A 16 in. wide specimen was used for the L-T test and a 6.3 in. wide specimen was used for the T-L test. The tests were run at full thickness and at room temperature lab air (18 to 28° C.). Anti-buckling guides are required.

TABLE 2 MECHANICAL PROPERTIES OF ALLOY A Age Time Yield Tensile at 290 F. Test Strength Strength Elongation (hrs.) Direction (ksi) (ksi) (%) 24 L 56.7 63.7 12 24 LT 56.25 66.05 10 48 L 64.3 69.3 10 48 LT 62.7 69.7 8

Fatigue crack growth (FCG) was measured The fatigue crack growth tests were run in accordance with ASTM E 647 using W=102 mm wide T-L orientation, middle-cracked tension M(T) specimen with a starting notch length of 2an=5.08 mm. Tests were run using a constant load amplitude covering a range of ΔK from about 10 to 45 MPa·√m with a stress ratio of R=0.1, and a testing frequency between 2 and 25 Hz. Tests are run in room temperature lab air (18 to 28° C.) with relative humidity greater than 20% and a maximum relative humidity of 55%.

The test data for Alloy A was compared to the incumbent fuselage skin alloy, Alclad 2524-T3, the result of which are illustrated in FIGS. 1-3, below. For the FCG testing, the test data shown are from M(T) specimens of the same geometry as the C77W specimen. The test was run in accordance with ASTM E 647 using a constant K gradient. The R-curve data shown for Alclad 2524 were run on M(T) specimens, W=16 in. and 2a/W=0.25.

While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure. 

1. A wrought aluminum alloy product having a thickness of from 0.040 inch to 0.500 inch, the aluminum alloy consisting of: from 3.00 to 3.80 wt. % Cu; from 0.05 to 0.35 wt. % Mg; from 0.975 to 1.385 wt. % Li; wherein −0.3*Mg−0.15Cu+1.65≦Li≦−0.3*Mg−0.15Cu+1.85; from 0.05 to 0.50 wt. % of at least one grain structure control element, wherein the at least one grain structure control element is selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof; up to 1.0 wt. % Zn; up to 1.0 wt. % Mn; up to 0.12 wt. % Si; up to 0.15 wt. % Fe; up to 0.15 wt. % Ti; up to 0.10 wt. % of any other element, with the total of these other elements not exceeding 0.35 wt. %; and the balance being aluminum. 2-5. (canceled)
 6. The aluminum alloy of claim 1, comprising at least 3.10 wt. % Cu.
 7. The aluminum alloy of claim 1, comprising at least 3.20 wt. % Cu.
 8. The aluminum alloy of claim 1, comprising at least 3.30 wt. % Cu.
 9. (canceled)
 10. The aluminum alloy of claim 1, comprising not greater than 3.75 wt. % Cu. 11.-12. (canceled)
 13. The aluminum alloy of claim 1, comprising not greater than 3.60 wt. % Cu.
 14. (canceled)
 15. The aluminum alloy of claim 1, comprising at least 0.15 wt. % Mg.
 16. The aluminum alloy of claim 1, comprising not greater than 0.30 wt. % Mg.
 17. The aluminum alloy of claim 1, comprising not greater than 0.25 wt. % Mg.
 18. The aluminum alloy of claim 1, comprising at least 1.005 wt. % Li. 19.-20. (canceled)
 21. The aluminum alloy of claim 1, comprising at least 1.150 wt. % Li.
 22. The aluminum alloy of claim 1, comprising not greater than 1.355 wt. % Li.
 23. (canceled)
 24. The aluminum alloy of claim 1, comprising not greater than 1.310 wt. % Li.
 25. (canceled)
 26. The aluminum alloy of claim 1, comprising at least 0.20 wt. % Zn.
 27. The aluminum alloy of claim 1, comprising at least 0.30 wt. % Zn.
 28. The aluminum alloy of claim 1, comprising not greater than 0.50 wt. % Zn.
 29. The aluminum alloy of claim 1, comprising not greater than 0.40 wt. % Zn. 30.-31. (canceled)
 32. The aluminum alloy of claim 1, comprising at least 0.15 wt. % Mn.
 33. The aluminum alloy of claim 1, comprising at least 0.20 wt. % Mn. 34.-37. (canceled)
 38. The aluminum alloy of claim 1, comprising not greater than 0.40 wt. % Mn. 39.-46. (canceled) 